The use of annular combustion chambers in axial flow gas turbine engines is a well known design feature which is particularly well suited for providing a high rate of heat release in a limited volume. Not only must such chambers provide an optimum combustion environment to ensure combustor efficiency and engine operability over a wide operating range, but they must also protect the surrounding engine structure from the contained high temperature combustion reaction.
As with any components used in the working gas stream of a gas turbine engine, and especially for those engines used in the air transport industry, a significant premium is placed on configurations having the features of light weight, simplicity of assembly, and the fewest individual components. Prior art combustion chambers have utilized an annular combustor head, supported by the outer engine casing, and adapted to receive a plurality of circumferentially distributed fuel nozzles therewithin. The head-nozzle structure is disposed immediately downstream of the engine axial compressor section, forming the leading edge of the combustion chamber defined by the head and two axially extending, concentric chamber liners disposed immediately downstream of the head.
The annular combustion zone formed by the head and combustor liners contains the combustion reaction and shields the engine inner and outer casings from the high temperature reaction. Both the head and inner and outer chamber liners are typically cooled by diverting portions of the annular air stream received from the compressor section.
During startup, shutdown, and other load transients the combustion chamber components may experience a wide variation of material temperatures. Such variations produce differing magnitudes of thermal expansion between the liners and head, requiring some form of accommodating joint or mounting in order to maintain sealing and/or structural integrity. The use of sliding expansion joints in combustion chambers is well known in the prior art, achieving both simplicity in design and assembly and providing the necessary flexible interaction between different components. Such sliding joints, however, are subject to separation between the concentric components as a result of an uneven axial or circumferential heat distribution. It will be appreciated by those skilled in the art of combusting systems that the admission of an unexpected and unpredictable flow of air into the combustion reaction as a result of such seal separation quickly degrades the quality and efficiency of the reaction.
What is needed is an expansion joint which is resistant to the wide temperature variations occurring in the combustion chamber and which is configured so as to reduce and minimize the effect of any leakage which may possibly occur.